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What can N-N-bar Oscillation teach us about physics Beyond the standard model ?

What can N-N-bar Oscillation teach us about physics Beyond the standard model ?. R. N. Mohapatra University of Maryland NANO workshop, February, 2011. Particle oscillations. Oscillations of quantum mechanical states is a familiar phenomenon in Nature.

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What can N-N-bar Oscillation teach us about physics Beyond the standard model ?

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  1. What can N-N-bar Oscillation teach us about physics Beyond the standard model ? R. N. Mohapatra University of Maryland NANO workshop, February, 2011 Theme Group 2

  2. Particle oscillations • Oscillations of quantum mechanical states is a familiar phenomenon in Nature. • In particle physics, electrically neutral particles e.g. Kaons and neutrinos have been observed to oscillate, teaching us a great deal about the fundamental forces and matter. • Neutron is a neutral particle- its oscillation to anti-neutrons is allowed by electric charge conservation . What can it teach us about physics beyond the standard model ?

  3. Neutron-anti-neutron Oscillation: • Violates baryon number by two units: • Any Indication of B-violation in Nature ? (i) Standard model has B-violation (but it leaves B-L symmetry exact and B-L is emerging as a new symmetry of Nature ) !! (ii) Understanding the origin of matter requires B-Violation and often involves B-L violation !! (iii) Most physics scenarios of physics BSM have B-violation e.g. Grand unified th. Mohapatra

  4. B-L : new symmetry in Nature ? • Is B-L symmetry of standard model exact ? • If not, what is the scale of its breaking ? • What physics associated with this breaking ? • Hints from neutrino observations: • If neutrino is Majorana, it breaks B-L by two units; observation of decay will confirm this but by itself will not tell us much about new physics associated with B-L breaking. • N-N-bar observation will supply this information !! Mohapatra

  5. Neutrino mass-NNbar connection • Majorana neutrino -> implies B-L=2; • In quark-lepton unified theories B and L get connected and L=2 implies B =2 via B-L symmetry and hence N-N-bar oscillation. • There are reasons to think that there may be quark lepton unification at high energies. • Discovery of neutrino mass therefore provides a very strong motivation to search for N-N-bar oscillation, which can be new window to Q-L unification as well as B-L symmetry.

  6. Questions for N-N-bar oscillation • Can the possible reach of N-N-bar oscillation time in existing facilities probe interesting range for new physics ? OR • Are there decent theories EMBEDDING THE SEESAW MECHANISM for small neutrino masses where a viable Seesaw scale leads to observable N-N-bar oscillation ? • Is it cosmologically safe to have observable N-N-bar oscillation ? • The answer to all these questions is YES .

  7. Operator analysis of N-N-bar To see what is probed by N-N-bar, do operator analysis for processes: Note M^5 suppression Theme Group 2

  8. Scale Reach of N-N-bar • Is the scale reach of N-N-bar limited to only upto 300 TeV in generic models as suggested ? • NO-once new physics at TeV scale is entertained e.g. SUSY, new Higgs !

  9. Weaker suppression with SUSY A. Dominant operator with SUSY: B.SUSY + diquark Higgs field , at TeV scale Can probe M_B-L upto 10^9 GeV Probe M_{B-L} to 10^12 GeV. Theme Group 2

  10. theory For N-N-bar • Neutrino mass points to New electroweak symmetry with B-L • Gauge group: Left-right sym th. • Fermion assignment: • Higgs fields:

  11. Probing B-L scale and related physics Note that SUSY at TEV SCALE + no new physics till GeV implies that coupling constants unify: This suggests that perhaps local B-L is part of a grand unifying symmetry and it breaks at GUT scale. Related physics is GUT physics. Theme Group 2

  12. B-L- GUT • (A): SO(10) : the minimal GUT theory with B-L motivated by Gauge coupling unification: • All fermions unified to one {16} dim rep. • Breaks to MSSM below 10^16 GeV; • B-L scale is GUT scale due to unification. N-N-bar suppressed and unobservable. Theme Group 2

  13. Nucleon Decay in Generic Signature • Key test of GUTS: Gauge Boson mediated p-decay: Lower life time predictions are highly model dependent. Theme Group 2

  14. Alternative B-L Unification • New physics below GUT scale • Only 16 fermions unified but not gauge couplings: 2. Cantains B-L for seesaw; Only restriction on B-L scale is nu mass (not coupling unification) and hence N-N-bar can be observable in this case ; No proton decay. Theme Group 2

  15. Non-SUSY G(224) and N-N-bar • That these models lead to observable nn-bar oscillation was pointed out inRNM, Marshak, 80. • vertex needed for baryogenesis . • With M= N-N-bar observable only if

  16. SUSY makes N-N-bar probe higher scales • Two points: • (i) naturally at 100 GeV scale due to accidental global symmetry caused by supersymmetry- • (ii) Power suppression is rather than 1/M^5 (as in non-susy case). Improves observability of N-N-bar osc. Theme Group 2

  17. Estimate of N-N-bar in Minimal 224 model: • New Feynman diagram for N-N-bar osc. Observable N-N-bar osc for M_seesaw~10^11 GeV. (Dutta, Mimura, RNM; PRL (2006) Theme Group 2

  18. Origin of matter in N-N-bar models • Usual argument : Early universe baryon asymmetry erased by fast N-N-bar being in equilibrium: --hard to generate baryons: NOT TRUE --e.g.NonSUSY NNbar model: No leptogenesis; Out of eq. temp for NNbar operator is: 10 TeV; New source of baryon asymmetry: post-sphaleron baryogenesis:Babu,RNM, Nasri PRL, (2006,2007); Theme Group 2

  19. Does baryon asymmetry  observable NN-bar ? • ObservableNN-bar, earlier matter asymmetry gets erased. • Must regenerate below sphaleron decoupling scale ~ 140 GeV. • 2224 model experienceadequate amount of matter  light color sextet Higgsobservable NN-bar. • Not theorem but very palusible. (Babu, Dev, RNM’09; Babu’s talk). Theme Group 2

  20. Other models that can be probed by Nnbar • Extra dimension models generically have lots of new physics around the TeV scale- could lead to NN-bar oscillation: • Warped models realistic models locate various fermions in 5th dim-NN-bar can be observable. (Winslow, Ng’10) • Similar conclusions for flat LED type models: ( Nussinov, Shrock; Gabadadze, Dvali) Non-observation or observation of Nnbar will throw light on these models too.

  21. Proton decay vs N-N-bar oscillation Theme Group 2

  22. Conclusion • With the discovery of neutrino mass the case for N-N-bar oscillation is a lot stronger now than before. Urge new search at the level of 10^10 sec to test for B-L seesaw scale less than 10^11 GeV vs GUT scale seesaw. • N-N-bar discovery will completely change the thinking on grand unification. • As far as Proton decay goes, predictions below 10^36 yrs are model dependent; while they should be done, the true value of P-decay as a test of GUT idea is the 10^36 yrs level search and should be the ultimate goal. Theme Group 2

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